Computers are used today to store vast amounts of information about anything conceivable. The data is stored in large data bases. Once the information is stored, it has to be found quickly when needed. One of the techniques used in data bases is the use of inverted lists.
Inverted lists are used in data bases to allow for fast searches. For example, in a hospital data base, a request may be issued to find all the records of patients allergic to penicillin. One slow way to get this information from the data base would be to search each and every one of the patient records, selecting the records with penicillin in the allergy field. A better way and a common practice in data bases is to maintain inverted lists in the data base. In this example, using an inverted list allows a list of all patients allergic to penicillin to be found relatively easily and quickly.
Unfortunately, inverted lists require a lot of storage, take a lot of time to create, and have to be efficiently organized to enable the data to be found quickly. Usually inverted lists take more storage space than the original data bases which they support. Most data bases use inverted lists for only selected data items and therefore allow for fast searches only on selected items.